Inquiry Question: What is
DNA
and how does its structure contribute to your traits?
Every cell in your body contains
DNA.
DNAis the instruction manual for everything that makes you 'you'.
At the end of this inquiry, you should be able to answer the following questions:
What is DNA?
What is a genetic code?
What are chromosomes?
What are genes?
Page 39 to 45 in your textbook will help you answer these questions about DNA.
Introduction
Figure 1 – The offspring of asexual reproduction are exact clones of the parent.
Figure 2 – DNA in the nucleus of every cell carries all of the information about the organism.
The previous section explained asexual and sexual reproduction. Both methods have advantages and disadvantages for the organisms that use each type of reproduction.
During the process of asexual reproduction, no new genetic material is introduced. The offspring is an exact copy or clone of its parent.
On the other hand, sexual reproduction is more complex. How can different species evolve from a common ancestor yet have such distinctive features? Geneticists have discovered that all domestic dogs (Canis familiaris) descend from
the wolf (Canis lupus). Even more impressive is that only about a 0.2 percent difference exists between their DNA. A poodle, a dachshund, a Papillion, and a St. Bernard certainly do not look like one another – and none certainly
looks like a wolf.
DNA Inside every cell in our bodies is the building block of life called DNA, or deoxyribonucleic acid.
DNA is the inherited material responsible for variation in all individuals. Each cell within a body has a nucleus that contains the DNA of that organism. The DNA is a double-helix strand up to 2 to 3 metres long that contains all the codes for
the unique traits, such as hair colour, eye colour, and blood type.
Watch
What does DNA look like? How does it work in the body? The video "DNA
Structure" illustrates the structure and chemical makeup of DNA.
Interactive
The BrainPop "DNA" illustrates the structure and chemical makeup of DNA. Remember, the structure of DNA is a special way of storing all of the information required to build and maintain an organism.
Watch the DNA video, then try some of the other interactive activities on this page.
Many people wonder how this one
molecule
, DNA, can pass so many traits to the offspring if the molecule is the same in all cells. Although it looks the same, a deeper look shows many codes lying within the double helix. One of the greatest achievements in the last century in science occurred
when Watson and Crick found that DNA carries a wide range of instructions by using four nitrogen-based chemicals (adenine, guanine, cytosine, and thiamine).
These four chemicals follow a rule:
Adenine (A) always pairs with Thymine (T)
Cytosine (C) always pairs with Guanine (G).
The genetic code is created by the limitless combinations of A to T and C to G.
Chromosomes
Approximately 3 billion pairs of genes occur in a human’s DNA. For it to fit into our cells, DNA is wound tightly into packages called chromosomes. All species have various numbers of chromosomes.
Chromosomes form pairs based on similar genes. Humans have 46 single chromosomes or 23 pairs of chromosomes. Some species of ants have as few as 2 chromosomes (1 pair) and other species, such as fern plants, have 768 chromosomes (384 pairs
of chromosomes).
Chromosomes are complex. Each chromosome is made up of many genes. A gene, or many genes, is the code that gives an organism its traits.
Watch
To understand the parts of the cell better, watch "What is a Chromosome?".
These two links will help you understand DNA, chromosomes, and traits.
A small proportion of a species may have a unique inherited trait of albinism. An albino has no colours, or pigments, on their body.
View the video "Why Are Some People Albino?" to learn about this fascinating inherited trait.
Genes
Chromosomes contain many genes. Genes are sections or segments of DNA located in chromosomes. They come in pairs. Genes store the genetic code. They are responsible for the inheritance of various traits.
They make the proteins that, in turn, produce the heritable traits such as hair colour, eye colour, freckles, and many other features. Genes can be considered to be dominant or recessive. An example of a trait is an organism’s blue eyes,
but think about the options in the colour blue. We know that blue eyes can range from very light blue to dark blue.
Pages 40 and 41 in your textbook will help you learn more about genes.
Watch
Watch the video "Genes vs DNA vs Chromosomes" to see the differences between genes, DNA, and chromosomes.
Watch the video "What is a Gene?" to learn more about genes and chromosomes.
Interactive
OK, do you have all that? The basis of sexual reproduction is that a mother and a father combine their genetic information when fertilization of an egg occurs. The most important unit of genetic information is DNA, because it is the DNA that holds everything
about that newly formed organism.
A mutation is any process that changes a DNA sequence. It is quite a common occurrence, fortunately, many of the changes are repaired by the cell. If a mutation in a sex cell (egg or sperm) cannot be repaired, the mutation will be passed down
to the offspring.
Mutations can also occur when chromosomes (one from each parent) are mixed during fertilization. Part of the chromosome may be deleted or extra DNA may be present, as in the case of Down Syndrome.
Interactive
Genetic Mutations
An organism's genetic information gets copied, moved, and modified quite often. All of these changes allow errors to occur. The errors can lead to mutations, or changes in the genetic information in a cell. If the mutation occurs somewhere important,
and in a location that gets copied over and over, the mutation can have quite a large impact on the organism.
Some mutations are helpful, some are harmful, and some have little or no impact.
